The interactions of electric fields with living cells is an important problem in both basic research and clinical science. Although the mechanism of intermediate strength electric field- to-cell interactions been described, the mechanism of weak field- to-cell interaction is not understood. The inability to sort out a mechanism may be due to a failure to properly isolate the inherent variables, not the lack of an effect. During the first two years of this program we have identified amplitude modulation of NAD(P)H oscillations (or metabolic resonance) as a robust experimental tool to detect weak field interactions with cells then linked it to a broad spectrum of physiological changes in cells (oxidant production, extraordinary lengthening, and DNA damage). Preliminary studies indicate that membrane channels participate in detecting weak electric fields. This is likely to be the same mechanism as the intermediate strength fields, except that the timing of the field must co-incide with endogenous intracellular oscillators to permit detection. Thus, we will test the hypothesis that phase-matched DC and AC electric fields induce metabolic resonance in leukocytes and tumor cells via the transmembrane signaling apparatus. The role(s) of plasma membrane potassium and calcium channels will be examined with a panel of pharmacologic reagents in dose-response studies. The participation of calcium in coupling electric fields to metabolic resonance will be tested using several complementary approaches. We will use cells from CD38 knock-out mice, calcium pump inhibitors, and second messenger blockers of the inositol trisphosphate and cyclic-ADP-ribose systems, to test the role of the calcium signaling apparatus in metabolic resonance and DNA damage. To test theoretical predictions, we will assess the distribution of ion channels during various cellular conditions. We will also employ high-speed microscopy, developed during the first two years of this program, to directly image changes in calcium signaling during exposure to phase-matched and phase- mismatched electric fields. To determine the mechanism linking electric fields to alterations in cell metabolism, we will also test the role of glucose transport in metabolic resonance. Thus, the molecular mechanism leading to metabolic resonance and downstream effects on superoxide release and DNA damage will be ascertained. We anticipate that these studies will broadly contribute to a fundamental understanding of how cells interpret extracellular signals. This, in turn, will identify the conditions that may permit cells to be damaged by weak extracellular electromagnetic fields. Moreover, the ability of electric fields to remotely influence cell shape and metabolism may be of broad importance in human health.